The present invention relates to a supporting and guiding device for power lines, e.g. hydraulic oil circuits and/or electric instrumentation circuits, for an excavation device, e.g. a hydromill, to be mounted preferably on cranes, cable-type excavators or drilling machines for creating diaphragms in the ground.
It is known that in the ground drilling industry, in particular in the diaphragm field, excavation devices are generally used which are handled by means of a cable-type hoisting device.
In the case of a hydromill, which is normally used for creating diaphragms, it is necessary to handle a series of power lines, such as, for example, hydraulic oil hoses and electric instrumentation and control cables, which are generally also inserted into hydraulic hoses or anyway have particular construction characteristics that make them compatible with the work site.
Said hoses and cables are wound around a drum of a drawworks which, by turning, winds or unwinds them as necessary based on the movements required for the excavation process.
When depths are significant, indicatively over 100 meters, the length and weight of the hoses may reach considerable values, thus making it necessary to guide and support them in order to prevent them from becoming entangled as they go up and down during the excavation process, as well as to avoid that an excessive pulling force, generated by their own weight, might cause excessive stretching of the hoses and cables, which in some cases might lead to undesired failures. In fact, said hoses and cables, if too elastic, will cause the handling system to no longer be able to promptly react to the wind/unwind commands issued by the drawworks drum, resulting in problems of incorrect winding.
In addition, again due to the weight of the hose itself, when said hoses are wound around the drawworks drum each hose coil is subject to heavy pressures generated by the weight of all the next coils which are wound over it.
As a result, the innermost coil, i.e. the smallest diameter one directly wound over the drum, is subject to a very high pressure.
It is therefore necessary to constrain said hoses to one another, so that they can be wound in an orderly manner without undergoing structural damage, such as compression, and to guide them in such a way as to avoid any entanglement between hoses and/or cables as they are being moved.
European patent EP0518292 has disclosed an excavation device, e.g. a hydromill, wherein the power line hoses are kept spaced and parallel by transversal bars secured along the hoses at regular intervals; said bars are kept at the proper distance by suitable profiled spacers, thus creating two supporting branches.
The terminals of the bars and the profiled spacers are run through by one cable per branch.
In order to prevent the spacer elements wound on the drum from becoming misaligned, they are fitted with a tooth and a recess having complementary shapes, such that they will match perfectly when wound on the drum.
Each profiled spacer already wound on the drum acts as a guide by directly coupling its own tooth to the matching recess of the spacer being wound; the latter, in its turn, will perform the same guiding function for the next spacer.
When the hoses are unwound into the excavation, the whole weight of the hoses and of the spacer elements is borne by the two side cables.
When the weight acting upon the cables becomes considerable as the excavation process goes on, the cables themselves are progressively stretched up to the point where the profiled spacers crowd together at the bottom due to their own weight.
In this condition, the spacer elements are no longer guided and can rotate about the cable's axis and take anomalous positions.
The rotation of said spacer elements may be caused by vibrations, which are always present during an excavation, or simply by movements of the drilling machine or of the tool thereof.
Rotation of the spacer elements is essentially due to their own shape; in fact, said elements are parallelepipedons lacking any axial symmetry, and therefore are subject to torques.
Following the rotation of one or more spacer elements, when the hoses are rewound on the drum it may happen that they get stuck on the idle pulley, thus preventing any further rewinding.
Likewise, in the section from the winding drum to the idle pulley at the top of the crane arm, it may happen that the spacer elements no longer in contact with each other get closer to each other after having undergone rotations, thereby taking an anomalous position.
Said anomalous position will prevent arranging the spacers in the appropriate configuration as they are wound on the drum.
Also, these rotations may create gaps between consecutive spacer elements, thus complicating, or even preventing, the step of pulling the hoses through the idle pulley.
It is also known, from European patent EP0708270, a support chain for a hose, which is used for guiding the hose that drains the mud and debris coming from the hydromill.
In the device described in European patent EP0708270, the hose spacing or guiding elements, which are preferably U-shaped, are run through by two side cables.
In this manner, any rotation of the guiding elements about the hose axis is prevented by the symmetry of the structure, due to the presence of specularly arranged cables.
In the operating configuration wherein the hose is at the bottom of a deep excavation, the weight borne by the two cables becomes substantial in relation to the strength of the cables themselves.
Under the action of this weight, the cables are subject to stretching that creates a gap, or interspace, between the idle pulley and the last hose guiding element, because the guiding elements slide along the cables under their own weight and get stacked one over the other at the bottom.
This sliding of the spacer elements is problematic, in that it may cause strong vibrations when the hose is recovered and, in some cases, it may cause one or more U-shaped elements, or even the idle pulley, to fail.
Finally, it is known from U.S. Pat. No. 7,845,154 a device adapted to guide and support the weight of a set of hoses for power lines, e.g. for a hydromill.
Said device is formed by two chain branches, connected by transversal bars to the hoses, which are kept at the desired distance by a series of spacer elements, each of which is run through by at least one pair of cables.
In the art prior to this patent, each branch is usually constituted by a single main supporting cable, inserted in the main hole.
Said patent makes an attempt to solve the problem of rotation of the spacer elements when the cable is wound on the drum or when the branch is suspended vertically along the excavation.
As described in the patent, in order to overcome this problem it is possible to insert into each branch a second cable, placed in a suitable hollow housing, for the purpose of preventing the elements from rotating.
In view of the function it performs, this second cable is always thinner than the main cable, because it must not bear any suspension or support load.
Said second cable also runs through all the spacer elements comprised in the branch.
Another problem arises in this case as regards the alignment and spacing of the spacer elements, which is due to the fact that, under the considerable weight of the hoses and of all the suspended parts, the absorption of axial loads by the two cables is inversely proportional to their rigidity.
The maximum stretching undergone by the two cables, however, will only be associated with that of the supporting cable.
When the absorption cables are stretched, the second cable, i.e. the thinner one, will turn out to be loose, thereby allowing the spacer elements to rotate about the hole corresponding to the axis of the supporting cable.
In addition, said solution does not solve the above-mentioned problem of the downward stacking of all the spacers present in the branches extending from the drawworks drum to the upper pulley of the crane arm.
This last patent does not even solve the problem of the repeated descent of the spacers into the excavation when the cable is progressively stretched and the spacers get stacked at the bottom, due to their own specific weight.